# Bottom Flange Access Hole Model \[STG] The first step in performing Access Hole-related checks is to define and generate the access hole within a **separate Steel Tub Girder project**. As outlined in the [Access Hole Design (STG)](https://github.com/openbrim/platform/blob/master/docs/documentation/templates/steel-tub-girder-bridge-workflow/superstructure-code-checks-stg/access-hole-design-stg/README.md), the analysis of access holes requires a **refined mesh** to ensure the Finite Element Analysis (FEA) is as accurate as possible. To maintain the simplicity and efficiency of the global bridge model, this separate project approach is the recommended method for modeling access holes. {% hint style="info" %} **Applying Loads and Analyzing Access Holes in Steel Tub Girders** Following the modeling step, the next phase involves applying the relevant loads, such as **axial loads**, to the access hole. This is done using the **Bottom Flange Access Hole Load** object. For detailed instructions on applying these loads, refer to the **Bottom Flange Access Hole Load** section in the documentation. This process ensures loads are applied accurately and consistently within the refined model. After performing the analysis, the **stress concentrations** and corresponding values can be displayed, providing a clear understanding of the localized effects caused by the access hole. {% endhint %} ## General The geometric properties of the access hole model for both 3D and FEM can be defined using the parameters on the General Tab. **Plate Length**: The plate length (in the X-axis direction on the global coordinate system) can be defined using this parameter. **Plate Width**: The plate width (in the Y-axis direction on the global coordinate system) can be defined using this parameter. **Plate Thickness**: The thickness of the plate (in the Z-axis direction on the global coordinate system) can be defined using this parameter. **Hole Diameter**: The diameter of the hole can be defined using this parameter. ![image-20241130-101522.png](https://openbrim.atlassian.net/wiki/download/attachments/2805694465/image-20241130-101522.png?api=v2) **Plate Material**: A material must be assigned to the access hole plate. Materials can either be imported or assigned from previously defined ones under **Properties > Materials**. The material properties will be directly used for FEA (Finite Element Analysis). **Mesh Size**: The mesh size definition is the maximum distance between two adjacent nodes. A larger mesh size results in a less refined FEM model. **Circle Segment**: This parameter specifies the number of segments used to generate circle of the access hole. A larger number for the circular segment would generate a smoother circle. ![image-20241130-102622.png](https://openbrim.atlassian.net/wiki/download/attachments/2805694465/image-20241130-102622.png?api=v2) ![image-20241130-102440.png](https://openbrim.atlassian.net/wiki/download/attachments/2805694465/image-20241130-102440.png?api=v2) **Mesh Option:** The generation of a mesh for FEM of the plate can be specified by this parameter. * **MeshAdapt** : Adapts the mesh during the simulation based on solution gradients for improved accuracy. * **Automatic** : Generates a mesh automatically with default settings, providing quick and simple results. * **Initial Mesh Only** : Generates only an initial mesh without further refinement or adaptation. * **Delaunay** : Uses Delaunay triangulation to create high-quality triangular (2D) or tetrahedral (3D) meshes for complex geometries. * **Frontal-Delaunay** : A variant of Delaunay that constructs the mesh incrementally using front-tracking for better element quality. * **BAMG** : A mesh generation method optimized for handling complex geometries, often with minimal user input. * **Frontal-Delaunay for Quads** : Applies the frontal Delaunay method specifically for quadrilateral meshes, often in 2D. * **Packing of Parallelograms** : Fills the domain with parallelogram-shaped elements, suitable for structured meshes. * **Quasi-structured Quad** : Generates a mostly structured quadrilateral mesh with some flexibility for irregular shapes. **Plate Chamfer (Length Direction):** Chamfer dimension applied at each corner of the plate in the length (X-axis) direction. Setting a non-zero value trims that distance off each end corner so the plate corners become chamfered rather than square, which helps match field-fabricated access-hole plates and reduces stress concentrations at the corners. **Plate Chamfer (Width Direction):** Chamfer dimension applied at each corner of the plate in the width (Y-axis) direction. Setting a non-zero value trims that distance off each side corner; combined with the length-direction chamfer, this produces the angled corner cut on all four corners of the plate. ## Access Hole **Access Holes:** List of individual access holes cut into the plate. Each list entry defines one hole with its own shape (Circle or Rectangle), diameter or length/width, corner radius (for rectangles), circle segment count, and X/Y offset from the plate center. Add one entry per hole you want to model; the plate 3D surface and the FE mesh are both updated to include each cutout. ## Left Edge Boundary Conditions For the left edge of the plate, the stiffness values to be applied to the nodes for translation along the axes Tx, Ty, Tz, and rotation along the axes Rx, Ry, Rz can be specified using the parameters in this tab. The stiffness values can be defined as either **Free** or **Fixed**, or by specifying values. **Tx \[Free/Fixed]**: Translation along the X-axis direction **Ty \[Free/Fixed]**: Translation along the Y-axis direction **Tz \[Free/Fixed]**: Translation along the Z-axis direction **Rx \[Free/Fixed]**: Rotation about the X-axis direction **Ry \[Free/Fixed]**: Rotation about the Y-axis direction **Rz \[Free/Fixed]**: Rotation about the Z-axis direction ## Right Edge Boundary Conditions For the right edge of the plate, the stiffness values to be applied to the nodes for translation along the axes Tx, Ty, Tz, and rotation along the axes Rx, Ry, Rz can be specified using the parameters in this tab. The stiffness values can be defined as either **Free** or **Fixed**, or by specifying values. **Tx \[Free/Fixed]**: Translation along the X-axis direction **Ty \[Free/Fixed]**: Translation along the Y-axis direction **Tz \[Free/Fixed]**: Translation along the Z-axis direction **Rx \[Free/Fixed]**: Rotation about the X-axis direction **Ry \[Free/Fixed]**: Rotation about the Y-axis direction **Rz \[Free/Fixed]**: Rotation about the Z-axis direction ## Top Edge Boundary Conditions For the top edge of the plate, the stiffness values to be applied to the nodes for translation along the axes Tx, Ty, Tz, and rotation along the axes Rx, Ry, Rz can be specified using the parameters in this tab. The stiffness values can be defined as either **Free** or **Fixed**, or by specifying values. **Tx \[Free/Fixed]**: Translation along the X-axis direction **Ty \[Free/Fixed]**: Translation along the Y-axis direction **Tz \[Free/Fixed]**: Translation along the Z-axis direction **Rx \[Free/Fixed]**: Rotation about the X-axis direction **Ry \[Free/Fixed]**: Rotation about the Y-axis direction **Rz \[Free/Fixed]**: Rotation about the Z-axis direction ## Bottom Edge Boundary Conditions For the bottom edge of the plate, the stiffness values to be applied to the nodes for translation along the axes Tx, Ty, Tz, and rotation along the axes Rx, Ry, Rz can be specified using the parameters in this tab. The stiffness values can be defined as either **Free** or **Fixed**, or by specifying values. **Tx \[Free/Fixed]**: Translation along the X-axis direction **Ty \[Free/Fixed]**: Translation along the Y-axis direction **Tz \[Free/Fixed]**: Translation along the Z-axis direction **Rx \[Free/Fixed]**: Rotation about the X-axis direction **Ry \[Free/Fixed]**: Rotation about the Y-axis direction **Rz \[Free/Fixed]**: Rotation about the Z-axis direction --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.openbrim.org/templates/steel-tub-girder-bridge-workflow/superstructures-code-check-stg/access-hole-design-stg/bottom-flange-access-hole-model-stg.md?ask= ``` The question should be specific, self-contained, and written in natural language. 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